[Pulmonary concentration of asbestos fibers in steel workers with pleural mesothelioma].

The asbestos fibre burden of the lung has been used in the past as a biological indicator of cumulative exposure to the mineral so much so that in 1997 reference limits even for non-occupationally exposed people have been proposed. This kind of analysis was performed on groups of workers of different type of industries and allowed to achieve a qualitative-quantitative estimate of past exposure to asbestos, even in absence of exposure estimates by environmental monitoring. An important example is the steel industry where asbestos was widely used in the past, but for which there are not available exposure estimates of workers. Among the mesothelioma cases collected by the Mesothelioma Registry of the Province of Brescia from 1980 to present there are 55 workers who spent at least 5 years in steel industry, on a total of 289 cases classified as asbestos exposed (19%). For 8 subjects who worked in steel mills and production of electrical steel pipes, of which 4 in the same plant, lung tissue samples were available for the asbestos fibres burden analysis (7 samples coming from autopsies and 1 from extra-pleural pneumonectomy). In all cases the diagnosis was given with histological analyses supplemented with immunohistochemistry. In 7 cases autopsied the diagnosis was confirmed. The work histories have been reconstructed in detail through the interview process, inclusive of details of duties performed. The asbestos fibre burden analyses showed a range of concentrations between 260,000 and 11,000,000 ff per grams of dry tissue; the concentration of amphiboles was much higher than that of chrysotile. The highest body burden was detected in the maintenance workers of the same plant in witch a cluster of malignant mesothelioma was observed. In conclusion, this study illustrates the results of asbestos fibres burden analyses in subjects where exposure to asbestos is sure but not quantifiable. The results showed also that these concentrations can reach values that overlap with those found in asbestos-cement workers and in asbestos-textile workers. These data suggest to consider the cases of mesothelioma occurred in the steel workers at least as "possible" exposure, even in the absence of adequate information on the circumstances of contact with asbestos. This study, although based on a small number of cases, is the only one ever held in Italy on workers in this sector.